How can I line up the bottom and top of photoetch fuel barrels/tanks (such as those on the JS-3) so they are an equal distance from each other and the lip of the barrel. I am talking about the two PE discs that fit on the top and bottom. The problem is that there are no grooves to help line up the discs in the barrel. Hope this makes sense.

I've never had to deal with this personally but a couple of solutions do come to mind.

The first one would be to cut some plastic rod to fit inside the barrels, 3 or 4 pieces all the same length glued to the inside of the barrel spaced to allow the top and bottom pieces to sit on the rod in the correct position.

The second one is similiar but instead use one piece of larger diameter plastic tube cut to the correct length. Glue it to one of the end pieces, then glue that piece to the barrel, when dry glue the other end on. I hope that makes sense.

Mike